Quantum Size Effects and Transport Phenomena in PbSe Quantum Wells and PbSe/EuS Superlattices

It is established that the room-temperature dependences of transport properties on the total thickness of PbSe layers d in PbSe/EuS superlattices exhibit an oscillatory behavior. It is shown that the oscillation period Δd practically coincides with the period of the thickness oscillations observed earlier in single PbSe/EuS quantum well. The non-monotonic character of these dependences is attributed to quantum size effects. The theoretically estimated and experimentally determined Δd values are in good agreement

Size effects in chlorine doped PbSe thin films

The possibility of obtaining strongly degenerate (≈ 3·10²⁰ сm⁻³) PbSe thin films (d = 5 – 220 nm) with n-type conductivity by thermal evaporation in vacuum of PbSe crystals doped with PbCl₂, with subsequent condensation onto (001) KCl substrates was established. It was shown that the films had high homogeneity degree, no grain structure was observed. The thickness dependences of thermoelectric properties (the Seebeck coefficient S, the Hall coefficient RH and the electric conductivity σ) of thin films were obtained. In the thickness range d ≈ 5 ÷ 30 nm, oscillation properties were observed with growth of d that are attributable to electron gas quantization. The calculation of S(d) dependence on the assumption of size quantization with regard to contribution of several subbands and the thickness dependence of the Fermi energy was shown to be in agreement with the experimental data. In the region of d > 30 nm there was growth of S and σ with thickness, which is attributable to manifestation of classical size effect and interpreted in the framework of Fuchs-Sondheimer and Mayer theories

Dependences of thermoelectric properties on the thickness of thin films of indium doped lead telluride

Dependences of thermoelectric properties (the Seebeck coefficient S, the electric conductivity σ, the Hall coefficient RH, the carrier mobilityμ and the thermoelectric power P = S²·σ) on the thickness d (d = 10 – 255 nm) of thin films prepared by vacuum evaporation of indiumdoped PbTe crystals and subsequent condensation on (111) BaF₂ substrates were obtained. With decreasing thickness of films to d ≈ 40 nm, there is n- to p-type inversion of conduction which is related to a change in thermodynamic equilibrium conditions and partial reevaporation of lead and/or indium atoms. Extremes were found on the thickness dependences of properties at d₁ ≈ 20 nm which is indicative of hole gas quantization. In the range of thicknesses with n-type conduction there is a smooth change in thermoelectric properties with thickness which testifies to manifestation of classical size effect and is sufficiently well described in the framework of the Fuchs-Sondheimer theory

Synthesis and properties of spherical catalysts TiO2-SiO2/МхOy (M = Co and Cr)

Layered spherical materials were obtained, the inner layer of which is represented by oxides of cobalt or chromium, and external oxides of titanium and silicon. D-metals were fixed on the surface of the polymer substrate through sorption from aqueous solutions of the corresponding salts. The outer layer of the oxide titanium-silicon matrix was obtained by the sol-gel method. Aggregative stability of sols was controlled by viscosimetry. The influence of the components on the stability of sol solutions has been established. The time interval for the stability of sols is in the range of 400-1000 h. The laminated structure, material characteristics are studied using 3D-microtomography. The catalytic activity of the obtained TiO2-SiO2/Cr2O3 and TiO2-SiO2/Co3O4 samples was compared to the n-heptane oxidation reaction. The maximum heptane conversion for the TiO2-SiO2/Co3O4 sample is 80 % at a temperature of 600 °C, for the TiO2-SiO2/Cr2O3 sample, the conversion of n-heptane reaches 100 % at 400 °C

Symmetries of Electrostatic Interaction between DNA Molecules

We study a model for pair interaction $U$ of DNA molecules generated by the discrete dipole moments of base-pairs and the charges of phosphate groups, and find noncommutative group of eighth order ${\cal S}$ of symmetries that leave $U$ invariant. We classify the minima using group ${\cal S}$ and employ numerical methods for finding them. The minima may correspond to several cholesteric phases, as well as phases formed by cross-like conformations of molecules at an angle close to $\rm{90}^{o}$, "snowflake phase". The results depend on the effective charge $Q$ of the phosphate group which can be modified by the polycations or the ions of metals. The snowflake phase could exist for $Q$ above the threshold $Q_C$. Below $Q_C$ there could be several cholesteric phases. Close to $Q_C$ the snowflake phase could change into the cholesteric one at constant distance between adjacent molecules.Comment: 13 pages, 4 figure

Vacuum fluctuation forces between ultra-thin films

We have investigated the role of the quantum size effects in the evaluation of the force caused by electromagnetic vacuum fluctuations between ultra-thin films, using the dielectric tensor derived from the particle in a box model. Comparison with the results obtained by adopting a continuum dielectric model shows that, for film thicknesses of 1-10 nm, the electron confinement causes changes in the force intensity with respect to the isotropic plasma model which range from 40% to few percent depending upon the film electron density and the film separation. The calculated force shows quantum size oscillations, which can be significant for film separation distances of several nanometers. The role of electron confinement in reducing the large distance Casimir force is discussed

Prediction of Anisotropic Single-Dirac-Cones in Bi1−x{}_{1-x}Sbx{}_{x} Thin Films

The electronic band structures of Bi${}_{1-x}$Sb${}_{x}$ thin films can be varied as a function of temperature, pressure, stoichiometry, film thickness and growth orientation. We here show how different anisotropic single-Dirac-cones can be constructed in a Bi${}_{1-x}$Sb${}_{x}$ thin film for different applications or research purposes. For predicting anisotropic single-Dirac-cones, we have developed an iterative-two-dimensional-two-band model to get a consistent inverse-effective-mass-tensor and band-gap, which can be used in a general two-dimensional system that has a non-parabolic dispersion relation as in a Bi${}_{1-x}$Sb${}_{x}$ thin film system

Transverse-momentum-dependent Multiplicities of Charged Hadrons in Muon-Deuteron Deep Inelastic Scattering

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality $Q^{2}>1$ (GeV/$c$)$^2$, invariant mass of the hadronic system $W > 5$ GeV/$c^2$, Bjorken scaling variable in the range $0.003 < x < 0.4$, fraction of the virtual photon energy carried by the hadron in the range $0.2 < z < 0.8$, square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 (GeV/$c)^2 < P_{\rm{hT}}^{2} < 3$ (GeV/$c$)$^2$. The multiplicities are presented as a function of $P_{\rm{hT}}^{2}$ in three-dimensional bins of $x$, $Q^2$, $z$ and compared to previous semi-inclusive measurements. We explore the small-$P_{\rm{hT}}^{2}$ region, i.e. $P_{\rm{hT}}^{2} < 1$ (GeV/$c$)$^2$, where hadron transverse momenta are expected to arise from non-perturbative effects, and also the domain of larger $P_{\rm{hT}}^{2}$, where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small $P_{\rm{hT}}^{2}$ to study the dependence of the average transverse momentum $\langle P_{\rm{hT}}^{2}\rangle$ on $x$, $Q^2$ and $z$. The power-law behaviour of the multiplicities at large $P_{\rm{hT}}^{2}$ is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.Comment: 28 pages, 20 figure

Лейкомогенный риск и темп накопления дозы радиационного воздействия. Сообщение 2: Сравнительный анализ лейкоцитарных индексов и динамики показателей периферической крови в зависимости от дозы внешнего гамма-облучения

The results of a retrospective analysis of leukocytic indices and dynamics of peripheral blood values in relation to external gamma-exposure dose among the personnel of the first atomic production facility in Russia were presented. The study was performed on the basis of the database “Leukemia in the cohort of workers of the Mayak Production Association employed in 1948-1958”. The database contains hematological, clinical and dosimetry information on the two groups of workers: the study group includes individuals with leukemia as the cause of death (n=84); control group includes personnel without hematological cancer pathology (n=300). The control group was composed by selecting 3-4 internal control cases for each leukemia case taking into account gender, age of the start of the exposure and the same accumulated absorbed dose of gamma-exposure to red bone marrow. Based on 19592 analysis of peripheral blood we had described hematopoiesis shifts along cell lines, performed correlation analysis of interrelation between hemogram values and radiation dose, analyzed particular characteristics of blast cells’ appearance in peripheral blood flow in the period prior to leukemias. Comparative analysis of various leukocytic indices was performed among Mayak PA personnel for the first time. The diverse nature of the response of bone marrow hematopoiesis was noted; more pronounced hematological shifts were indicated regarding more intensive production exposure. A number of hematopoietic features were detected among people exposed to production radiation: 1) cytopenia in relation to minimum accumulated doses of radiation exposure in both studied groups; 2) more pronounced lability of hemograms in relation to increased accumulation dose of external gamma-exposure and period of radiation exposure among individuals who had developed leukemia in future in comparison to controls; 3) correlation between peripheral blood cells and accumulated doses of external gamma-exposure was characterized by the highest values of coefficients among individuals with future leukemias; 4) myeloblasts were most often registered among all the blast cells; proerythroblasts were characterized by the shortest average period from the start of the exposure and to the moment of their appearance in the peripheral blood flow (178 days in the study group); polychromatophile erythroblasts in peripheral blood were registered only among the workers with future leukemia; 5) when comparing leukocytic indices in proportion to the categories of accumulated doses of external gamma-exposure, a pronounced variability in the ratio of blood cells was observed among exposed individuals who were subsequently diagnosed with leukemia, especially in the range of 2.0-2.5 Gy. Thus, a comprehensive analysis of hematological parameters, including the assessment of leukocytic indices, is more informative than studying a standard hemogram. Particular features of the dynamics of the cellular composition of peripheral blood can be used as indicators of pathological hematopoiesis in exposed workers prior to clinical manifestation of leukemia.Представлены результаты ретроспективного анализа лейкоцитарных индексов и динамики показателей периферической крови в зависимости от дозы внешнего гамма-облучения среди персонала первого в стране предприятия атомной отрасли. Исследование проведено на основе базы данных «Лейкозы в когорте персонала производственного объединения «Маяк» 1948–1958 гг. найма». База данных включает гематологическую, клиническую и дозиметрическую информацию о двух группах работников предприятия: в основную группу вошли лица, причиной смерти которых был лейкоз (n=84); в группу сравнения – персонал без онкогематологической патологии (n=300). Формирование группы сравнения произведено подбором 3–4 внутренних контролей к каждому случаю лейкоза с учетом пола, возраста начала облучения и той же накопленной поглощенной дозы внешнего гамма-облучения на красный костный мозг. На основе 19 592 анализов периферической крови описаны сдвиги гемопоэза по клеточным линиям, проведен корреляционный анализ взаимосвязи между показателями гемограммы и дозой радиационного воздействия, проанализированы особенности появления в периферическом кровотоке бластных клеток в период, предшествующий лейкозам. Впервые среди персонала «Маяка» проведен сравнительный анализ различных лейкоцитарных индексов. Отмечен разноплановый характер реагирования костномозгового кроветворения, показаны более выраженные гематологические сдвиги при более интенсивном производственном облучении. Выявлен ряд особенностей гемопоэза среди облученных на производстве лиц: 1) цитопения при минимальных накопленных дозах радиационного воздействия в обеих исследуемых группах; 2) более выраженная лабильность гемограмм с увеличением накопленной дозы внешнего гамма-облучения и периода радиационного воздействия среди лиц, заболевших в дальнейшем лейкозами, по сравнению с контролем; 3) корреляционная взаимосвязь между клетками периферической крови и накопленными дозами внешнего гамма-облучения характеризовалась наибольшими значениями коэффициентов среди лиц с последующими лейкемиями; 4) среди бластных клеток наиболее часто регистрировались миелобласты; проэритробласты характеризовались самым коротким средним периодом от момента начала облучения до их появления в периферическом кровотоке (в основной группе – 178 дней); полихроматофильные эритробласты в периферической крови были зарегистрированы только среди персонала с лейкемиями в дальнейшем; 5) при сравнении лейкоцитарных индексов пропорционально категориям накопленных доз внешнего гамма-облучения отмечена выраженная вариабельность соотношения клеток крови среди облученных лиц, у которых впоследствии диагностирован лейкоз, особенно в диапазоне 2,0–2,5 Гр. Таким образом, комплексный анализ гематологических показателей, включая оценку лейкоцитарных индексов, является более информативным, чем изучение обычной гемограммы. Особенности динамики клеточного состава периферической крови могут служить индикаторами патологического кроветворения у облученных работников до клинической манифестации лейкемий